of the total rural population in many countries. As a sweeping generalization, it may be said that the social structures of such communities are ill-adapted to cope with the comparatively sudden and sizeable increase in population. Wolf (25) has made an interesting comparison of "closed corporate peasant communities" in two widely separated world areas, Central Java and Meso-america. The ability of these communities to absorb additional numbers and their mode of accommodation will depend upon many factors, including availability of raw land, the land tenure arrangement, and the labor requirements of the agricultural system. In a fascinating study, Geertz (26) shows how Javanese villagers have accommodated population increase by agricultural "involution," made possible by the considerable elasticity of labor input that the wet-rice system permits. The social system adjusts to the increased numbers by the practice of "shared poverty." However effective this adjustment may be over the short term, the long-term consequences are indeed grim. In any event, most peasant societies do not have available to them the flexibility of the wet-rice system. One major form of adaptation to increasing rates of natural increase, and doubtless the most universal one, is out-migration. Sometimes it is likened to a safety valve that works to prevent population pressure on local resources from building up to a danger point. The analogy is a dangerous one, for it implies that out-migration works like an automatic control device. It is anything but that. Anyone who tries to make sense of rural out-migration rates, such as they are for developing countries, soon must acknowledge that they are not to be explained in any mechanistic fashion. Although rural-urban migration is widespread and well-known, it is still difficult to get reasonably satisfactory statistics on the movement. In any event, migration flows in themselves are insufficient. One better way to evaluate the significance of rural out-migration is in terms of the concept of the "reservoir" of potential rural out-migrants. Barraclough (27) reports some interesting estimates made for seven countries of Latin America. First it was assumed that the out-migration from rural areas that was destined for urban areas represented about one half of the natural increase in the rural areas for the 1950-1960 period. This net rural-urban migration was then stated as the percent of the 1950 rural population of the country. The countries and their percentages are given below: Chile 29.0% Argentina 24.9 Brazil 19.0 Ecuador 17.0 Colombia 16.6 Peru 13.6 Guatemala 3.6nounced rise in the rate of natural increase has resulted. This in turn has meant an increase, in various degrees and various ways, of population pressure on resources (24).